Pass URL to Browser::new(), delegate url checking logic to 3rd party
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1. Move the logic of computing the initial url from `opts.rs` to `/ports/servo/main.rs`
2. Add a `ServoUrl` argument to `Browser::new`
Based on the requested changes by @paulrouget:
>We can read the pref in main() instead. shell.homepage would be used if the url is not passed as an argument. I'm trying to decouple the "app" logic and the "web engine" logic. I think it's up to the app to set the initial URL, and I'm not sure the initial url should be part of opts.
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Report more informative CSS errors
This requires https://github.com/servo/rust-cssparser/pull/143 for the final commit. There's no better way to split that work up, unfortunately, and it's extremely easy to bitrot. I would appreciate if we could expedite reviewing this work.
This is the work necessary to enable https://bugzilla.mozilla.org/show_bug.cgi?id=1352669. It makes sense to merge it separately because it's so much effort to keep it up to date with the ongoing Stylo work.
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Reduce code duplication when adding a SessionHistoryChange
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Implemented add_pending_change method and refactored code to use this new method
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Bug1368610 - stylo: implement primitive (bit, uXX) type of discrete animatable properties
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This PR is to fix https://bugzilla.mozilla.org/show_bug.cgi?id=1368610
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